Power generating stations produce tremendous amounts of thermal energy. These stations generally use cooling systems to reduce or eliminate thermal heat, thereby keeping the plant at a suitable temperature during accidents and normal plant operation. However, these normal cooling methods are unavailable to remove residual (decay) heat during plant maintenance periods. Therefore, there is a need for a system to sufficiently cool the system to allow maintenance personnel to access and fix piping, wiring and instrumentation problems.
The current method for heat removal is to directly cut into and interface with the system loop piping so that a separate temporary system can be attached to circulate the internal fluid between the heat source and a heat exchanger. Referring to FIG. 1A, incisions G are made in the system piping C and temporary piping D is installed. A specially designed pump E and heat exchanger F are attached to the temporary piping. The pump E and heat exchanger F are specially designed (e.g., canned parts) to accommodate the flow of radioactive coolant. The normal flow path through the heat source (core) is used to cool the heat source. However, direct interface with system loop piping is particularly undesirable in Duclear power plant systems because 1) the work is time consuming resulting in excessive human exposure to higher radiation levels, and 2) the difficulty associated with containing radioactive fluid. Therefore, a non-intrusive method, which removes heat from nuclear power plant systems without cutting into the system piping, is desired. There is no way to directly cool the pressure vessel containing the nuclear fuel constituting the heat source. The system needs to utilize a heat exchanger located on the adjunct piping system which will cool the heat source. The system must rely on natural circulation of the internal fluid to transfer heat from the source to the heat exchanger.
Several types of non-intrusive heat exchangers currently exist which could be attached to the pipe, and these were considered for this application. One method uses commercially available clamp-on heat exchanger cooling jackets. The cooling jackets consist of two sheetmetal plates spaced to create an air gap between and to create an air gap around the system pipe curvature. The plates are edge-sealed and are spot welded together with a weld pattern that produces a dimpled or embossed surface on the outer plate. This raised embossment array provides for homogenous mixing of the coolant, as it passes through the cooling jacket. Couplant is applied to the pipe surface, prior to installing the cooling jackets, to transfer cold temperature from the cooling jacket to the pipe. However, this process is messy and the amount of heat extracted is inadequate.
Another method uses clamshell type covers. These covers are configured to provide a sufficient gap between the inside surface of the shell and the exterior surface of the pipe. The covers are then axially and circumferentially sealed when installed onto the pipe, but had a major disadvantage in requiring the shell to become flooded and necessitating pressure-tight seals between the pipe and exterior shells.
Therefore, there is a need to remove heat from nuclear power plant system piping in a non-intrusive manner while avoiding the disadvantages of the prior art. This invention would provide non-intrusive heat removal that is clean, provides adequate heat removal and uses commercially available parts.